Code signal regenerator



ug.'3, 1954 A. LlGuoRl 2,685,613

CODE SIGNAL REGENERATOR Filed Jan. 14, 1952 4 Sheets-Sheet 2 MMMATTORNEY All@ 3, 1954 `A. LlGUoRl y 2,685,613

I CODE SIGNAL REGENERATOR l 4 y Filed Jan. 14, 1952 4 Sheets-Sheet 3 f5van @Le .n 161?.

* f4 /A/far ef L v /5 V25 a9 f c /P/d wl Y Tw /2 i C7, 'gf r van V5 -c aT 5 l "a 'a Aug 3, 1954r A. LIGUoRl 2,685,613

coDE SIGNAL REGENERATOR Filed Jan. 14, 1952 4 sheets-sheet 4 ATTORNEYPatented Aug. 3, 1954 conc SIGNAL REGENERATOR Anthony Liguori, New York,N. Y., asslgnor to Radio Corporation of America, a corporation ofDelaware Application January 14, 1952, Serial No. 266,386

The terminal fifteen years of the term of the patent tobe granted hasbeen disclaimed 15 Claims.

The invention relates to telegraph signalling circuits, and particularlyto circuit arrangements for regenerating distorted telegraph signals toa form satisfactory for application to printers or other code handlingapparatus.

'Regenerators or regenerative repeaters are known which are partelectronic and part electromechanical. In such regenerators theelectromechanical portion usually consists of relays, or brushessweeping over faceplates, or both. A large degree of maintenance isnecessary in such electro-mechanical portions to insure satisfactoryoperation at all times. Another disadvantage of the prior artregenerator arrangements is that the outgoing circuit is often closed inthe absence of incoming signals or upon faulty operation of theregenerator itself as a result of which the attention of a Yskilledoperator `is required.

Therefore, Ait is an object of the invention to provide an improvedelectronic circuit for regenerating code signals which is completelyautomatic and free from mechanical, operating and maintenancedifculties.

yIt is another object of the invention to provide an improved electroniccircuit which automatically presents spacing signals to the outgoingline in the absence of received Ysignals or upon faulty operation Vofany part of the regenerator circuitry.

Itv is a more specic object of the invention to provide an improvedcompletely automatic electronic circuit which accepts distorted 5-unit,1.41-stop-pulse telegraph printer signals and automatically retransmitsundistorted signals.

A further object of the invention is to provide lan improved timingcircuit for use with startstop telegraph signal regenerators and likearrangements Which is stable and accurate in operation While readilyadjustable to diierent conditions vof operation.

The objects of the invention are achieved in a circuit arrangement in`which the received signals are automatically applied to an integratingmark/space detector and output signals corresponding to the receivedsignals are regenerated in the detector and automatically vconnected byelectronic switching means to output terminals.

The mark/space detector determines the nan ture of the signal element tobe regenerated by charging a capacitor during spacing intervals only. Ifa charge corresponding to a predetermined percentage of a baud elementis developed across the capacitor the element is `assumed to have 'beenspacing. If the charge isless than the predetermined amount, the elementis assumed to have been marking. Reading of the charge on the capacitoris eiected at the end of each signal element as determined by thearrival of a pulse from a local timing unit. The start of theregenerated element occurs exactly one baud element after the start ofthe received signal element. In other words, the regenerated signal isone baud element 'behind the incoming signal in time.

Since the local timing unit is set into operation by the rst transitionfrom mark-to-space, that is, supposedly the beginning of the startpulse, any transition occurring when the local timing unit is notactive, whether caused by the start pulse or by a burst of interference,will cause the regenerator to start cycling.

A false start detector is provided to prevent the regenerator fromcycling when a signal other than a true start pulse is received. This isaccomplished by comparing the charge on the integrating capacitor with afixed voltage. Insufficient charge on the integrating capacitor resultsin the formation of a pulse which prevents the timing unit from cycling.

An output signal selector is employed to apply the proper signal rto theoutput terminals Vunder all conditions. Under normal conditions,

the regenerated signal is connected through an electronic switch to theoutput terminals. During conditions of solid marking or solid spacing,the input signal is connected through the electronic switch to theoutput terminals. Included in this section are circuits to apply spacingsignal elements to the output terminals in case of failure of componentsin the regenerator.

A feature of the invention is a timing unit comprising a lockingcircuit, hereafter called the timing control circuit, a start-stoposcillator and a counting chain. The received start pulse triggers thetiming control circuitY and `starts the oscillator. 'The counting chaincounts a predetermined number of complete cycles and restores thetimingcontrol circuit and stops the oscillator. Any speed o' operationcan be achieved by the proper choice of oscillator frequency.

The invention will be described in detail with reference to theaccompanying drawing forming part of the specification and in which;

Fig. 1 is a functional diagram of a vsignal regenerator circuitarrangement according to the invention;

Fig. 2 is a schematic diagram of a preferred electronic circuitarrangement .according to the invention for performing `the functionsillustrated in Fig. 1; and

Fig 3 is a graphical representation of pertinent waveforms developed inthe circuit arrangement shown in Fig. 2.

Referring to Fig. 1 there is shown a functional diagram of a code signalregenerator according to the invention wherein received 5-unit signalsare applied to an input stage I5 having output connections to an outputsignal selector l2 incorporating electronic switch circuitry selectivelyto connect the signals from the input stage I to an output stage i4 forutilization in known manner. Alternately, the signal from the inputstage I is connected through the electronic switching circuitry in theoutput signal selector I2 to a mark/space detector IE and from which aregenerated output signal is applied to an output stage I4. A timingunit, IB synchronized by a connection to the input stage II), isarranged to provide properly timed waves for actuating the elements ofthe system in proper phase relationship and a false start detector I9 iscoupled between the mark/space detector I and the timing unit I3 toprevent cycling on short spurious bursts of interference.

The following detailed description ci a preferred circuit arrangementfor performing the above described function is presented in somewhatdifferent order to more clearly set forth the inter-relationship betweenthe componentsA It should also be understood that while the fol-- lowingdescription for convenience is based on a 5-unit, 1.4-stop-pulse code,it is within the scope of the invention to accommodate any xed lengthcode having one signal element of length greater than the remainingelements.

The input stage Il) is shown, in the upper left corner of Fig. 2b, byway of example only as a triode tube VIA having a resistor RI in thegrid circuit, across which the incoming signal is applied. In practicethe incoming signal is of negative polarity for marking elements andZero potential for spacing elements so that the triode tube VEA isconducting only on spacing elements thereby producing a train ofpositive pulses corresponding to the marking elements of the incomingsignal. It is to be clearly understood, however, that any form of inputstage may be used, consistent with the signal to be handled, to providepositive polarity output pulses corresponding to mark signal elements.

The 5-unit, start-stop printer signal is composed of seven pulses. Fiveof these pulses identify the character being transmitted, and two pulsesare provided for synchronizing purposes, namely, a start pulse and astop pulse. The start pulse and the live signal pulses are of unitlength or time duration, and the stop pulse is approximately 1.41 timesunit length or time duration to allow for speed differences between thetransmitting and the receiving apparatus. Hereinafter, each pulse ofunit length is termed a baud element or baudel for convenience.

TIMING UNIT The function of the timing unit i8 is to generate a train ofeight timing pulses equally spaced in time; the time spacing being equalto one baud element or baudel This is accomplished by a bistablereciproconductive circuit, hereinafter called the timing control circuitand a timing wave generating circuit comprising, a start-stop oscillatorand a chain of pulse counting circuits. A start pulse obtained from theincoming signal is applied to the timing control circuit to trigger thesame to a given state of conduction and start the oscillator. The chainof counting circuits are effective to count seven complete cycles of theoscillator output, whereupon the timing control circuit is triggered tothe complementary or reciprocal state of conduction, and stop theoscillator. Any speed of operation can be obtained by proper choice ofoscillator frequency.

The timing unit I3 as shown in detail in Fig. 2a, comprises a timingcontrol circuit Ii, a start-stop oscillator 182, a limiting or clippingstage I S3, and three bistable reciproconductive binary counter circuitsI-I81- The timing control circuit I8! comprises two triode tubes VIB andVSB arranged in a known reciproconductive circuit which is perhaps morefamiliarly termed a bistable multivibrator circuit and is sometimesreferred to as a locking circuit.

Under static conditions, referred to hereinafter as the idle condition,the tube VSB will be conducting and the tube V'IB will be blocked. Inthis condition, the anode of the tube V'IB is very much positive withrespect to -B. This positive potential is applied through the voltagedivider comprising two resistors R31 and RSR to the grid of anoscillator control tube VIiB causing that tube to conduct. When theoscile later control circuit comprising the tube VI IB is conducting, apositive potential is developed across a resistor R58. This developedpotential is applied to the grid of a triode tube VIBB, which inconjunction with another triode tube VHA and associated componentsconstitute the two-terminal oscillator ISZ. Application of positivevoltage to the grid of the tube VIZB causes a large amount of current toflow through a re istor R66, tube V|2B and through the oscillator coilL. This current flow saturates the coil L and causes oscillation tocease immediately. The tube VI2A is blocked by the positive voltagedeveloped across the resistor R56. By careful selection of the value ofthe resistor R555, the prope1' value of positive voltage will be appliedto the grid of the tube VI2B to provide the correct amount of currentflow through the tube VIZB, and all transients will be minimized. Whenthe tube VI IB is blocked, that is, no current flowing through theresistor R63, oscillations begin immediately at maximum amplitude. Theaction of this oscillator is more fully described in U. S. Patent2,505,368 issued April 25, 1950, to E. R. Shenk and A. Liguori.

In the idle condition, the tube VIIA is also nonconducting since thegrid of the tube Vi iA is tied to the grid of the tube VIB through a reSistor RMZ. This removes the -B supply from one grid return of each ofthe three bistable reciproconductive circuits it-|81. Removal of Bcauses the grids of the tubes VA, VISA, and VI5B to be returned to -I-B,to maintain tubes Va'A, VI BA and Vi 5B conducting and the countercircuits locked in that condition. This clamping circuit is necessary toprevent random conduction of these circuits so that the proper count canbe had at all times.

Tubes VISA and VMA are two stages of amplication and clipping. Theoutput of the two terminal oscillator 182, developed across R64 issquared up and applied as square waves to the rst stage |85 of thebinary counting chain by way of capacitors C25 and C26.

When a negative pulse from the tube VEA is applied by way of a capacitorC9 (Fig. 2b) to the grid of tube V813, that tube is cut oir and thecomplementary tube VlB conducts. This aises-,ois

state 'of conduction isfknowni as the acti-Mercendition; Therionly;function of the. pulses from .the :tubeVIA through the vcapacitor 0951sto block ithetube V833: it is' conducting. The: pulses .cannot cause thetube VSB to conductzunder .any circumstance.

As-.the anode of the tube V'i'Br goesi'negative and the tubeVIxlBzisblocked, -causing the oscil- .flaitor |182 to'begin oscillatingimmediately. When :the Atube 'Vl'B starts tok conduct,v the -counterresetting. tube VI'IA :starts to conduct andthis ret-urns -B'ctovzthegrid'V return l'resistors of. the ztubes -VSAVIUA .andVlEBgj The binarychain isthus :ready tofstartcolmting. The action of .binary'counters is-well known and will not be described in detail. p

The blocking of current`ow' through; the .re-

n sis'tor Rtrcausesthe tubeV'IZA to conduct. Re-

moval of current flow trom the coil L causes fthe tank ycircuitvcomprising the coil L .andthe capacitor C22 to 'oscillate immediately.As VIZA conducts, anegative voltage is developed across 'the resistorRdandapplied .to the grid of the clipping tube VISA. This tends tocutoff the tube VIBAandxthev anode of the tubeVI3A goes positive. `Sincethe :grid of .the tube VI4A is tied through a resistor RTI. to `theanode of the' tube V'IBA,v the tube VVI'lIA conducts` and a negativevoltage is developed across an .anode resistor 4'Rl-3 and vapplied tothebinary counting chain. Thus at the beginning of .the first cycle a`negative :pulse is applied to the binary chain. At the end ofthe firstcycle, since the'tube VI2A is .starting to I.conduct again, anothernegative puise is'applied to .the binary chain. The binary chain fisfarranged .to .count eight `pulses before a negative pulse isforthcoming from the anode ci the tube-VSA. It takes seven full cyclesof the oscillator to produce eight negative pulses. At theeighthnegativelpulse applied to the binary chain, .thenegative pulsedeveloped at the anodeof the .tube VA is applied to the grid of the tubeV'IB to block the Asarne .and cause 'the-tube VEB to conduct.,VV Thisvis the idle condi.tionand"the circuits return to the initial state asexplained before.

Since in this instance seven full cycles are required, three stages ofbinary counters areused but it is obvious that'any number of counting:stagescan be used to achieve any desired count.

v'Since the negative pulses are created when the voltage across the tankcircuit is going through nero, there is substantially no energy in thetank circuit so there is essentially no transient response. tion of itscycle results in energy being left in the .tank circuit causingtransient response.

The comple-te action is thus seen to be; the first negative pulse fromthe tube'VIA through the capacitor C9 triggers the timing controlcircuit I8! permitting the oscillator |32 to cycle lseven times and thena negative pulse from the tube VSA applied through the capacitor C12restores the timing control circuit tothe initial or idle condition. Thesquare Waves generated by the tube VIGA across the resistor R13 are alsoapplied to the mark/space detector I@ through a capacitor C314.

is to determine Whether a given baud element or baudel of input signalis to be regenerated as -a .marking or. aspacing element. This is done'by charging al capacitor .during spacing intervals i Stoppingtheoscillator at any other por- `:.-L

only.: If achargewcorresponding to a predeter- :mined percentage .of abaudel. is developed across the .capacitanA the baudel is. assumed tovhave been a spacing element. If the charge isv less than thepredetermined amount, the baudel is assumed to havebeen a markingelement. The ycharge on the capacitor is read at the end of each-signalbaudel as determined by .the arrival of .a pulse romthe local timing.unit I8; The

.start fof .the regenerated vbaudel occurs exactly.

one :baudel .after the :start of .the received signal baudel. In otherwords, the regenerated signal isone baudel behind the incoming signal intime.

The .mark/space detector as shown in detail inig. 2c, is a modiiicationof the circuit de'- :scribed in the .copending U. S. patent applicationSerial No. 106,998 iiled July 27, 1949, of L. J. v@oldi-Tischer (now U.S. Patent 2,606,975 issued August l2, 1952) forfAn Integrating'Type'Tele- .graph Signal Detector.

The received signals are fed from the input amplifier tube VIA (Fig. 2b)to the grid' of a lowl impedance generator tube VISA to drive a triodeVZilA. When the tube V2 DA is conducting, -aconstan-t current generatortube V2 IA is blocked. 'When the tube VZA is blocked the tube VZ-IA ispassing a current lof constant amplitude' to a signal elementintegrating capacitor C28. When the irl-put signal baudel is yspacingthe capacitor C28 is charged Vby the flow of current from the tube VZIA.

At the end of every baudel, a phase inverter tube VZEB, which has squarewaves obtained from the timing unit I8 applied to the grid, generatestwo pulses of opposite polarity. 'Ihe positive 4pulse is applied to thegrid of a take-out tube V2'5A. Ii' the integrating Ycapacitor C28 hasbeen 4su-iiicientl-y charged so that the anode of the tube V2IA is morenegative than ground, the tube V2-5A will conduct when the positivepulse is applied to the grid of the tube V25A and a capacitor C3I willbe charged to the sameV value as the integrating capacitor C28. Thecapacitor CSI is very small compa-red to the integrating capacitor C28.This negative voltage developed across the capacitor 'C'3I is applied tothe vgrid of a tube VZIB through a capacitor Ct and a positive pulseappears at the anode of the tube VEI-B. This i-s known as the spacingpulse and tends toV vtrigger `a bistable reciproconductive or lockingcircuit referred to hereinafter as the regeneratedsigna-l circuit |68 tothe `spacing vcondition i-n which the tube VZBB is conducting. The time:constant of a parallel circuit comprising a resistor lRI-IQ and thecapacitor CSI tends to elongate the duration of the pulse so that it isvery long compared to the pulse applied to vthe grid of the tube ViiA.

I-f the integrating capacitor C23 is positive when the: local positivepulsey is applied to the .grid vof Ithe tube VZEA, no charge isdeveloped across :the capacitor C31, and, therefore, "no spacing pulseis generated.

Simultaneousvvith fthe application of the .pulse .to the grid of thev:tube V255., a negative. pulse is applied to a triode V293.whichcontro'ls a `clearyout pentode .tube V22.. Thecornbi-nation ofresistors Riti?, Rite, Rit@ vand RIN is .arranged to -tend tokeep vthegrid of the triode V2.0B-.posi tive, except that grid current keeps Ithegrid clamped to -B. The negative pulse from the -cathodewof the tube-VMEwhen applied to a time delay network comprising the resistor combinationpreviously mentioned, and the ycapacitors C33f`and.C2.9:, is .delayedlong Aenough to allow a capacitor C3I in the anode of the take-out tubeV25A to charge completely. The negative pulse then blocks the triode VZBcompletely for a very short time. A positive pulse, called the markingpulse is generated across a pair of series connected resistors RISS andRlll and applied to the regenerated signal circuit IBB tending totrigger the same to the condition in which the tube V23A is conducting.While the tube VZDB is blocked the pentode V22 conducts and almostcompletely removes the charge from the integrating capacitor C23. In theabsence of the spacing pulse, the marking pulse triggers the regeneratedsignal circuit |68 to the marking condition. Ii both pulses are present,the spacing pulse prevails since it begins earlier and ends later.

The triode V24A is connected to the timing control circuit I8 in suchmanner that when the latter is in the active condition the tube VZGA isconducting, and a slight negative voltage is present on the grid of thetube VZGB. This negative voltage due to the action of the clamping tubeV 24A keeps the tube VZBB from conducting fully and the grid of thepentode V22 in the anode circuit of the tube V2iIB is clamped at avoltage more positive than ground. Clamping the grid of the tube V22 ata positive voltage will keep the integrating capacitor C28 from everbeing charged to a negative voltage during idle condition. This is doneto eliminate any residual accumulative eiect so that the pulse generatedat the beginning of the rst cycle of the timing oscillator IGZ does notproduce a spacing pulse.

Clamping the anode circuit of the tube VZIBB at a positive voltageduring idle condition, also clamps the regenerated signal circuit E68 inthe marking condition. Thus the regenerator develops a stop baudel in amarking sense independent of the polarity of the stop baudel actuallyreceived.

The incoming signal is reproduced in regenerated form at the output ofthe regenerated signal circuit 68 of the mark/space detector IE and isapplied by means of the output signal selector !2 to the output stageI4.

OUTPUT SIGNAL SELECTORl The function of the output signal selector I2 isto supply the proper signal to the output stage y III under allconditions. Under normal conditions, the regenerated signal from themark/ space detector IE is connected through electronic switch circuitryI22 comprising triodes VSA, V3B, VA and V413 the output terminals forapplication to the output stage I4, which is not shown in detail sinceany of the conventional telegraph circuit output stages may be connectedto the switch output terminals I3, I3. During conditions of solidmarking or solid spacing, the input signal is connected through theoutput signal selecting electronic switch circuitry directly to theoutput terminals i3, I3. Also included in this section are circuits tocause the output stage to operate in the spacing or idle condition incase oi failure of components in the regenerator.

The output signal selector as shown in the upper portion of Fig. 2bselects the signal to be presented to the output stage, under any of thecircumstances listed below:

(a) Normal operation;

(b) Solid marking or solid spacing input signal;

(c) Failure of the timing unit I8;

(d) Failure of the mark/space detector I6.

Under normal operation the timing unit I8 and the mark/space detector I6function as previously described. The activation of the timing controlcircuit I8 brings into operation an output switch control circuit,comprising tubes VIA, V3A and V3B. The grid of the tube V3B is held atapproximately +25 volts with respect to ground. It should be morepositive than the anode of the tube V23B when conducting. The tube V3Bwill conduct when the cathode is more negative than +25 volts, but whenthe cathode is much more positive than --I-25 volts, the tube cannotconduct. The cathode of the tube V3B is connected to the anode of thetube V23B with the result that when the tube V23B is conducting, thetube V3B is also conducting.

The cathode of the tube V3A is connected to the input amplier tube VIAby way of cascaded amplier tubes VIB, V2A and V2B. 'I'he tube V3Afunctions in the same manner as does the tube V3B except that when thetiming control circuit is activated and the anode voltage of the tubeV'IA is reduced to approximately B, the tube V3A cannot conduct, sincethe grid of the tube V3A is connected to the anode of the tube V'IA. Assoon as V'IA is conducting, a capacitor C2 charges through the tube V'IAand resistors RI'I and RIS. When the timing control circuit isinactivated or idle, the tube V'IA stops conducting and the charge onthe capacitor C2 begins to discharge through a resistor RIB. The timeconstant of the parallel circuit comprising the resistor RIS and thecapacitor C2 is sumciently long so that if the timing control circuit isreactivated within to 200 milliseconds, the charge on the capacitor C2is sufficient to keep the tube VSA blocked. Ordinarily, therefore, ifautomatic transmission of the signal is employed, the tube VBA iscontinuously blocked so there is no switching involved and signal iscontinuously transmitted from the tube V23B by way of the switching tubeV3B to the output terminals leading to an output stage I4 which is shownin Fig. 1, but not in Fig. 2, since any conventional stage may be used.

When the input signal is solid marking, the regenerator proper is notincluded in the path from the input stage IIJ to the output stage Iii.The path is from the tube ViA through the tubes VIB, V2A, V2B and V3Aand their associated components, to the output stage It. When the inputis negative which is marking, the tube VIA is blocked and the tube VI Bis conducting with the anode driven negative so that the tube V2A is outoff. The cathode of the tube V2A will be essentially at ground potentialsince the capacitor CI has no charge, The voltage divider comprising theresistors RI 3 and RM is selected to main tain VZB at cutoi. The anodeof the tube V23B and the cathode of the tube VSA are at -I-B so nocurrent flows through the resistor RIB. The idle condition of the tubeV23B is also non-conducting so that the anode and cathode of V3B are at-I-B. Thus no current iiows through the tube V3B either. In the markingsense no cui1m rent is passing through the output load resistor Ri 6 andno potential is then applied to the output stage.

If the input signal is solid spacing, that is, no voltage, the tube VIAwill conduct causing the tube VI B to be blocked. The anode of the tubeV IB and the grid of the tube V2A then reach +B. Since the resistor RII)in the cathode circuit of the tube V2A has a high value of resistance,the tube acts as a cathode follower and the capacitor ages-merci Clischarged througli the tube V2A to almost'y +B. Consequently;y the' tubeYV235` will "conduct" andlthe anode togethervvith the cathodei of theKtube VBA dropfvery. close to g-roundpotential; If' thetiming unit IBhas: been idle for'rnore than about ZOOimilliseeonds, thegrid of? thetube VSA will"` @approximately-b2b volts; Thetube' VA' will conductthrough the, tube V23 and" the 'resistor Rlit. In tl-ieidle-or'spacingcondition;

rentfisV passing through the output2 loaol'res'i'stcr R16' and'potential'v is` applied to'.v4 the? stage I`4;

In casethe signalfiskeying and the timing conoutput'A trol circuit 181is inactive for' any. reason at.

first transitionl from marking to spacing; .the capacitor Clchargedthrouglffiv the'A tube V2A in a' Verys-hort; time. When the signal'r'evertsto marking, the capacitorr Ci' begins discharging through theresistors Rill; R11-, Ri?, l'ti3 andi R'I'dz- However, the timevconstantof' thisportionof the circuit is very long so the tube Vvvilllconduct -for about.Y 1251- milliseconds afterr input signaljhad revertedto. marking. lllhe outputsignai will bethe'same for an input of solidspacing.

Thisinsures thatkeyingsignalswill fnot be passedi f from-"input stagel'to-the output terminals and:

then'to the output stage lf Without being'regenerated.

Also includedy in. thel unit are' two failure noti!- cation circuitsE25, |23; These circuits` apply potentialitofthe outputstate lil intheevent' of failure ofthe' timing unit 13 or failure in the mark/space'detector iii. The tubes VSA'andVB supply notice of fail-urel in thetiming unit- 8. Once the'timing-controlcirciut t8! has been activated',one vof' the-functionsy of the timing' unit' iii is: to'supply apulseatthe' proper time to deactivate the timing controlA circuit i 8- i'. anyofi the components involved may causefthe timing control circuit lltoremain-active. While the timingv control circuitj idle; theftube. VGA

is conducting'an'd the' capacitor CS'is charged toV nearly -Byandf thetube- WIB is hel-d blocked.' Vli-en-the'timing control circuit itl isactivated,

the tube VBA is blocked andzthgcapaeitor @311s L discharged" throughv aresistorI R-and ifthe timingcontrol circuit lill remainszidle longer'than.v

they time: required to'regenerate one'character (about250 millisecondsor more), the capacitor Cial wil-1 have dischargedfsuiciently'tofalflowthe tube VAB to conduct andi-pass current? thr'ougl'if` the outputresistor Rit. Thisl is the idle. or spacing condition; The cli'argimg.rtime for the'capacitorf G3fis=very-shortfso that if the timingcontrolcircuitlis idle for only a few milliseconds; the# capacitoriCewill l"bef completely.` charged.

The second failure notification circuit` H23V includes `the tubes Vrin,VEA', VSB, VA',-V5B and assoc-iated components:

conducting and the voltage developed across.A the resistor B2b holdsxthetube VAA blocked. The capaz-:itery CilJ is chargedthroughlthe tube V'Aand the resistor R2 i1 Thel tube VEB rn'ayor not beconducting5dependingv on the 'condition ofthe regenerator outputindicating. reciproconducev tiveY circuit i241' .comprising thetubesVtii vand VSB. Whether the tube vsn is:@ontlasting1or.,isy

non-conducting has 'no eectf ontlie operation of the cfi-rcuitlat thisLtime. As soon as: the timing.

Failure of When the timing control" circuit` i8 iv isvin its idlecondition. the tube VA-is.-

control circuit Il is activated, thetubeiVilisY cut-off. Apulsefromtheanode ofthe tube WB issallied through 'a' capacitor' C2itoi'thel! grid-"off` the tube VA so that if thatttubewasfconducting.itfis'noiv blocked-f If.thetubefVAfwerefblockd 75.

'voutput load resistor Riti.

it remains so. rEhe gridfof the tube"Vlt'issconl1 nested tothe grid ofthetube'VGA so that the' former conducts Whenthelatter conducts;`Sine-e. both tub'esVAf and V 5B=are blockedgithe capacitor Cil starts'to discharge.l through'th'e' resistors. R25 and R26. The time.yconstant' of portion of the circuit.' is' such that' when approximately1-1/3 baud elements-have' elapsed; the tubeVA starts 17o-conductpasseur-renti through. the.

after the timing control circuit t8 I; has been triggered; to the activecondi-tions, the: regenerated start baud' element should cause the tubeVRSB? to conduct. The?negative-voltagedevelopedacrossv the't resisterRNE (Fig. 2c) isapplied asa pulsel through a' capacitor Cl (Fig'Zb)tothe grid ofv the tube VSB blocking the latter, indicating properoutputfrom the mark/space detector I9, and' causing' thetube Vil-Aand,therefore, tube; VSB to conduct.

sencefof thenegative pulse from the tube V233 indicates a probablefailure in the mark/space ldetector It, and the' tube VLlA isvpermitted-t0 conduct-fandf-thereby indicate such'failure by theVabsence. of potentialsacross ther output terminalsit, is.- Consequently,if signals are supplied'tov the input terminals but are not beingproperly'A l regenerated becausevof failurein the mark/space detectort6, then the output signal Will-consistV of almost sm complete baudelementsV of. spacing followed bya marking stop baud element; Thiscorresponds tothe transmitted character blank FALSE START DETECTOR Sincethe regenerator is set into operation by the iirst transitionfromgmark-to-spaca-that is,Y supposedly the beginning of'. the startbaud element the remote apparatus always puts solid mark on the linetoestablish thecircu-it before transmitting the rst start element, anytransition occurring when the regenerator is -notfactiva monostablerecproconductive circuit |91 (Fig. 2b) is' triggered in the false `startdetector Iii-asy shown? in. detail in the lower portion of Fig.. 2b.

This reciproconductive circuit` comprising. tubes VlliB andai/2SAremains in the triggered or une stablecohdition-for approximately 75percent of a-baudel.'. As the monostable reeiproconductive circuit MI.vreturnsv tothe stablecondition, a posi--l tivepulseof;fixedfampltitudeis generated.and applied to a comparing circuit 93 This companinglcircuit ist. is also; coupled'lto the spacing signal integrating;capacitor C-B'flig'. 2c). The

comparing circuit .E93 (Fig. 2b) comparesythe integrating.l capacitorvC231.- If' the magnitude of' thernegative'l biasl is` greater thanv`the# an-ipltudeY of: thefpositive'y pulse;` the rtiming con-trol.lcircuit f lltfis allowed tof remainlii'fthe' aotivefcoridition."

On conducting,v the tube .VoB restores the charge on the'eapacit'or C4beforev the tubeVA has--had-'time to conduct. The'a'b` .amplitude-ofthepositive pulseY with increasecin.I bias due totheincreasingnagativecharge.on'theV l l f the bias is insuicient to block thepositive pulse, the timing control circuit is deactivated or returned tothe idle condition thereby.

The false start detector I 9 is shown in detail in the lower portion ofFig. 2b. The tubes VQSA and VIAB constitute the monostablereciproconductive circuit I9! with the tube Vl 4B normally conductingand the tube V25A held nonconducting by the negative voltage developedacross a resistor RI28.

As soon as a negative pulse from the input tube Vl A is applied throughthe capacitor C9 triggers the timing control circuit IBI, a negativevoltage is developed across the resistor R3 Fig. 2a and applied througha capacitor C38, a resistor RI26 and a capacitor C35 as a negative pulseto the grid circuit of the tube VMB. This pulse triggers the monostablereciproconductive circuit ISI to the unstable state with the tube V25Aconducting and the tube VI4B blocked. The duration of this unstablecondition is limited by the time constant involving the circuitcomprising the capacitor C35, and the resistors RI2'I, Ri3 l RI32 andRI33, which are given values so that the circuit I9! is restored afterapproximately '75 per cent of a baudel. When the reciproconductivecircuit ISI is restored, a positive pulse is generated and appliedthrough the capacitor C36 and the resistor RI34 to the comparing circuit|93 comprising the tube V25B, and the resistors RI35, RISE and RIS'I.The tube V25B is connected as a cathode follower, and the grid thereofis connected to the oating end of the integrating capacitor C28. Thevoltage on the cathode of the tube V25B follows the voltage on the grid.The voltage divider comprising the resistors RI35, RISE and RISI dividesthe voltage in such a manner that when the cathode of the tube V25B isat essentially +B, the tube VISB is just biased to the cut-off point. Asthe capacitor C28 is charged and the cathode of the tube V25B becomesless positive, the bias on the grid of the tube V! 9B is increased. Therelationship between the charging voltage on the integrating capacitorC28 and the increase in bias on the tube VI 9B is the ratio of theparallel combination of the resistance of resistor RI36 and that of theresistor RIS'I to that of the resistor Rl35 plus the parallelcombination of the resistors RI36 and RIS'I.

If the integrating capacitor C28 has been sufciently charged so thatspacing pulse can be generated by the tube VZEA, then the increase inbias on the tube VIQB is suiciently large to prevent the xed amplitudepositive pulse which is applied thereto from causing the tube VIQB toconduct. If the integrating capacitor C28 has not been suicientlycharged, the positive pulse to the grid of the tube VlQB overrides thebias and the tube VI9B will become conducting, if the input signalelement is not a spacing element at that instant. A negative voltage isdeveloped across the resistor R!38 and applied through the capacitor C31as a negative pulse to the grid of the tube VIB. This pulse blocks thetube V'IB thereby restoring the timing control circuit I SI to the idlecondition.

TheV tube V26B and its associated components comprise a gating circuitIBG. The cathode of the tube VISB is connected to the anode of the tubeVB. As long as the tube V2SB is nonconducting, the cathode of the tubeVI 9B is returned to +B through the resistor RMI, thus since the anodeand the cathode of the tube VISB are returned to the same potentialthere can be no anode current flow. When the tube V26B is conducting,the cathode of the tube VI9B is con-a nected to ground through the tubeVZEB. This puts the tube VIEB in a position to conduct if a suicientlylarge positive pulse is applied to the grid. The tube VZBB conducts onlywhen the input signal element is a marking element. It does not conductwhen the input signal element is a spacing element. This prevents thetiming control circuit from being restored to the idle condition whilethe input is spacing. This feature coupled with other features to beexplained later act to notify the operator of apparatus connected to theoutput stage I4 of breakdown or failure in certain portions of theregenerator.

The activation and the subsequent inactivation of the timing controlcircuit I8I by the false start detector I9 all take place before thenominal end of the first baud element, so that in the event of a falsestart, everything has been inactivated before any signal has beenapplied to the output stage I4.

Mention was previously made of the gating effect of the tube V2 EB inthe false start detector I9 and which coupled with other circuits wouldact to notify the operator of breakdown of certain portions of theregenerator. Assume something is wrong with the regenerator somewherebetween the junction of the resistors R3, Ril and the integratingcapacitor C28, in such a manner that the capacitor C28 can never becharged no matter what the input signal. If the tube V26B was not in thecircuit and the cathode of the tube VIQB was connected directly toground, then approximately 3A; baud time after the timingl controlcircuit I8! is activated the pulse from the tube VIQB restores thetiming control circuit i8! to the idle condition. The operator has noidea of anything being amiss because the input of the output stage Illwould be a permanent marking signal. By inserting the tube VZBB in thecircuit as shown, the false start detector I9 cannot deactivate thetiming control circuit I8i if the input is spacing so the circuitremains active for a full character. Since the integrating capacitor C28cannot be charged, no spacingpulse can be created by the action of thetube V25A and the tube V23A continues to conduct. Since a negative pulsefrom the tube V23B is required to block the tube VSB, the absence ofthis pulse permits the tube VILA to conduct and show spacing output tothe output stage I4.

Fig. 3 shows the wave forms appearing at different points of the circuitduring the regeneration of two successive received characters, R and Yas expressed in 5unit code. The stop baud element is shown as 1.4 timesas long as the other elements.

Curve 3l represents the received signal RY in terms of input potential,a perfect signal being shown so that the action of the regenerator canbe more readily understood. In the diagram, positive is up and negativeis down.

Curve 32 represents the voltage at the anode of tube VSB. When it ispositive the timing control circuit IBI is active and when it isnegative the circuit is idle.

Curve 33 represents the seven cycles of output from the oscillator I82.

Curve 35 represents the negative timing pulses applied to the mark/spacedetector I6, from the timing unit I8.

Curve 3S represents the charge accumulating on the integrating capacitorC28 during the time the input signal is spacing.

Curve SIrepresents the spacing pulses derived trom-.the charge on the.integrating capacitor vit. These pulses appear at vtime end `ofeach-spacing lzfauclE element and arefformed by' the application'. ofthepulse's 4.shown curve sfthrough the tube VHB-to the gridot'the-tube-VZ'A.. These spacing pulses are negativeatthe anode oilthetube and positive 'at-the anode. ot 'the' tube VTIB.

Curve 3Erepresentsthe'marking pulses formed bythe application ofi the.pulses; in curve 35, throught'he tube'VZBland- .the-.delay circuit inthegrid of thertubeVZDB. 'Ther-'eis a mark-r ing' pulsefor everypulsegenerated by the timing unit'. t0.'- Thesemarking pulses startlater than the spacing pulses and end earlier.

Curve ail'l'representsthe regenerated .signalwhi'ch is identicalas'shown hereto the input sig'- nal except that it is displaced? one'.baud element in. time.

'IHef operating potential .for the circuit arrangementshown inI Fi'g.-2f may be supplied in any known-manner.- I-n. an actually constructedembodiment twoseparate regulated' rectifier unitslwere employed: onehaving the positive terminal connected to` +B and? thenegative Vterminalconnected vto ground delivering 150 volts Y regulated 'atY 22 ma.- andthe other'having the negative terminal connected to -B and..the-positive terminal a't ground delivering 1150 volts regulated/atv2`3-ma. A tapon the latter rectifierY unit-provided -200 volts.unregulated at 3 ma. fori connection to'- --C'. The screen grid of thepentode tube- V252 maybe connected to` a tap on theunregulated pcrtionofthe first rectifier unit toprovide a higher screenvoltage to insurecompletedischarge of the integrating capacitor C20 if that isfoundnecessary.

ln the above nlentioned-r embodiment actually constructed and operated,the following component-part values were employed for'operation ori-5'-unit=, 1'.4 stop pulse printer cocleat 60 words per minute:

REFERENCE NO. VALUE Resistors- RL. 100 kilohms. RSL; 240'- K. Y

ELL- 820 K. f RI`U` 820- K. Riff 1 megolini; .HIL 820K.

itl-3- 270K.

ated form, 'having' an input circuit coupled to said-input- Rl3l'.; 910K.` H1321.v 180 K'. R|33` 910 'K'. R430 180K. Ri3'5 L3 M. R`36 1.2V MLRi3T 1 M. R|33` 560 K. Rlll 1500 Capacitors.

Cl 0.2 uf C2 0.03 C3 0.05. C4 0.02. C1 0.0005 C8 0.0005 CS 0.0005 C221.61 ,uf C25 0.001 C28 0.075 C20 0.001

C31! 0.003 C3`5 0.01 C36 0.002 C37 0.0005 C3t 0.0005r Inductor L 7.5henry.

Tubes VLA, Vi1?" v 12AX7. V2A, VEB to VHA, ViZB IZAU'T.'

VISA, VSB', VM'A, VI'AB 12`AX7. VESA, V! 5B to VlA, VZi'B 12AX'7'. V226AQ5. V2`3A, V233 to VZBA, V263 12AU7L`v The circuit arrangement of Fig.2 was operated. at andY 100r Words per minute: with tllevalues otthevcritical component capacitors as listed. below:

- Obviously other keying speeds may be accom--A nioclatedVV by thecircuit arrangement as disclosed on changing the values of thekcomponent parts as will be evident to those skilledk in the art.V

The invention claimed is:

1. An electronic `circuit arrangement for re`- generating fixed length,vmark/space, telegraph signals of the'type whereinv oneV signal element'of eachcharacterv is of different length than the' other-signal'elements, including a; pair oi' inputl terminals'rtoA which the` signalsas received'are applied andv apair of output terminals from whichsaid'signals'Y are available in regener-f including a mark/spacedetector` terminals and an output circuit arranged` to produce markVvand space pulses. in. accordance.

with` the nature of.. the signal elements-applied.

tothe input circuit; output. signal' selecting electronic switch circuitarranged tov couple said out-- putv terminals. selectively.v to saidinput terminals *andv to the output circuitry of said mark/spacedetector, an electronic timing control .circuit arf ranged togheactivatedinresponseto the receipt of thnrst signalleler'nent of eachcharacter; an

. Mfd. Mid.l

0.010@ l 0.01231' e l. 01.60 0.055V 0.032

electronic output signal selecting switch control circuit coupled tosaid timing control circuit and said output signal selecting electronicswitch circuit to cause said output signal selecting electronic switchcircuit to couple said output circuit of the mark/space detector to saidoutput terminals when said timing control circuit is active and tocouple said input terminals to said output terminals for directoperation when said timing control circuit is idle, said output signalselecting switch control circuit incorporating a time delay whereby saidcoupling for direct operation is accomplished only after a prearrangedtime period after said timing control circuit is inactivated, a pulselengthening circuit interposed in said direct connections between saidinput and said output terminals to extend the spacing between markpulses as received at said input terminals, a further mark/spacedetector circuit arranged to determine the nature of said iirst signalelement only and to inactivate said timing control circuit when saidiirst signal element is of nature Opposite to that to which said timingcontrol circuit is arranged to respond, a circuit connection connectingsaid input terminals to said further mark/space detector circuit tonullify action thereof when the input signal element under considerationis of said opposite nature at the time of detection, another electronicswitch connected across said output terminals for indicating failure ofsaid timing control circuit and timing circuit failure switch controlcircuit incorporating another time delay connected between said timingcontrcl circuit and said other electronic switch and arranged to closesaid other electronic switch after another predetermined time periodafter said timing control circuit is activated, said other predeterminedtime period being greater than the time duration of one character ofsaid incoming signal, a further electronic switch connected across saidoutput terminals for indicating mark/space detecting failure and adetector failure switch control circuit having a time delay connectedbetween said timing control circuit and said further electronic switchand arranged to close said further electronic switch after a prearrangedtime period after said timing control circuit is activated, saidprearranged time period being greater than the duration of one signalelement of said incoming signal, and a timing wave generating circuitcoupled to said timing control circuit to produce a timing wave having anumber of cycles equal to the number of elements in each signalcharacter in response to the activation of said timing control circuit,said timing control circuit being inactivated on the last cycle of saidtiming wave.

2. An electronic circuit arrangement for regenerating fixed length,mark/space, start-stop telegraph signals of the type having a stopsignal element longer than the other signal element of each character,including a pair of input terminals to which the signals are applied asreceived and a pair of output terminals from which said signals areavailable in regenerated form, including a mark/space detector having aninput circuit coupled to said input terminals and a bistablereciproconductive circuit arranged to produce niark and space pulses inaccordance with the nature of the signal elements applied to the inputcircuit of the mark/space detector, an output signal selecting switchelectronic switch circuit arranged to couple said output terminalsselectively to said input terminals and to said bistablereciproconductive circuit, timing control bistable reciproconductivecircuit arranged to be triggered to an active state in response to thereceipt of the rst signal element of each character, an electronicoutput signal selecting switch control circuit coupled to said timingcontrol reciproconductive circuit and said output signal selectingelectronic switch circuit to cause said electronic switch circuit tocouple the rst said bistable reciproconductive circuit to said outputterminals when said timing control reciproconductive circuit is activeand to couple said input terminals to said output terminals for directoperation when said timing control reciproconductive circuit is in theidle state, said output signal selecting switch control circuitincorporating a time delay whereby said coupling for direct operation isaccomplished only after a prearranged time period after said otherreciproconductive circuit is inactivated, a pulse lengthening circuitinterposed in said direct connections between said input and said outputterminals to extend the spacing between marl; pulses as received at saidinput terminals, a false-start detector arranged to determine the natureof said first signal element only and to inactivate said timing controlreciproconductive circuit when said rst signal element is of natureopposite to that to which said other reciproconductive circuit isarranged to respond, a circuit connection connecting said inputterminals to said false-start detector to nullify action thereof whenthe input signal element under consideration is of said opposite natureat the time of detection, another electronic switch connected acrosssaid output terminals to indicate failure of the timing control circuitand another switch control circuit incorporating another time delayconnected between said timing control reciproconductive circuit and saidother electronic switch and arranged to close said other electronicswitch after another predetermined time period after said timing controlreciproconductive circuit is activated, said other predetermined timeperiod being greater than the time duration of one character of saidincoming signal, a further electronic switch connected across saidoutput terminals for indicating failure oi' the mark/space detector anda detector failure switch control circuit having a time delay connectedbetween said timing control reciproconductive circuit and said otherelectronic switch and arranged to close said further electronic switchafter a prearranged time period after said timing controlreciproconductive circuit is activated, said prearranged time periodbeing greater than the duration of one signal element of said incomingsignal, and a timing wave generating circuit coupled to said timingcontrol reciproconductive circuit to produce a timing wave having anumber of cycles equal to the number of elements in each signalcharacter in response to the activation of said timing oontrolreciproconductive circuit, said timing control reciproconductive circuitbeing inactivated on the last cycle of said timing wave.

3. An electronic circuit arrangement for regenerating xed length,mark/space, telegraph signals of the type wherein one signal element ofeach character is of different length than the other signal elements,including a pair of input terminals to which the signals as received areapplied and a pair oi output terminals from which said signals areavailable in regenerated form, including a mark/space detector having aninput circuit `coupled tolsaid input terminals and an output circuitarranged to produce mark and space pulses in accordance with. the.natureof. the signal elements applied to the input circuit, an outputsignal selecting electronic. switch circuit arranged to couple saidoutput terminals selectively to saidv input terminals and tothe outputcircuit oi said mark/space detector, an electronic timing; controlcircuit arranged to be activated' in response to thereceipt ofthe firstsignal element of each: character, an electronic signal selecting switchcontrol circuit coupledy to said timing control circuit and said output:signal selecting electron-ic switch circuit to cause the latterelectronic switch circuit to couple said output circuit of themark/space detector to said output terminals when' said tim-L Y. controlcircuit is active and to couple said input'terminals to said outputterminals for direct. operation when said timing control circuitv isidle, said signal selecting switch controlI circuit incorporating a timevdela-y whereby: said coupling for direct operationisaccomplished onlyafterr a prearranged time period after said timing controlI oircuit isinactivated,7 timing circuit failure electronic switch connected acrosssaid output terminals and a timing circuit failure switch controlcircuit incorporating another time delay connected between. said timingcontrol circuit and said timing circuit failure electronic switch andarranged to close the latter electronicv switch after anotherpredetermined time period after timing control circuit is activated,said other predetermined time period being. greater than the timeduration of one character of said incorning: signal, a detector failureelectronic switch connected across said output terminals and a detectorfailure switchcontrol circuit havingL a timek delay connected betweensaid timing control circuit and said detector failure-electronic switchandI arranged to. close the latter electronic switch after a prearrangedtimeperiod after said timing control circuit is activated', saidvprearranged time period being greater than the duration of one signalelement ot said; incoming signal, and a timing wave generatingcircuitcoupled to said timing control circuit. to produce a timing wavehaving. aI number of cycles equal tothe number of elements in: eachsignal character i'n response to the activation. of said timing controlcircuit, said timing control circuit being inactivated on theflast cycleof. said-timing wave.

4; An electronic. circuit. arrangement for regenerating xed lengthmark/space telegraph signals of the type wherein one signal element ofeach character isv of different length than the other signal elements,including a pair of input terminals to which the signals as received areapp-lied and a pair of output terminals from which said signals areavailable in regenerated form, including a mark/space detector having aninput circuit coupled tosaid input. terminals and an output-circuitarranged toproduceniarh and space pulses in accordance with thel natureof the signal elements' applied to the input circuit, a, circuitselecting electronic switcharranged to couple. said: outputA terminalsselectively to said input terminals and to the outp-ut circuit of saidmark/space detector; a timing control circuit arranged to be activatedinV response to the receipt ofl the nrst. signal. element of eachcharacter a circuitselecting.v electronic switch control circuit coupledto said' timing control. circuit and to said circuit selectingelectronic switch tocause the latter electronicl switch tol couple saidoutput circuit of. themarlr/space'detector to said output terminals'whensaid: timing. control! circuit is active and to couplev said inputterminals to said output terminals for. direct operation when saidtiming control circuit is idle, said circuit select,- ing switch controlcircuit incorporating a time delay whereby said coupling for directoperation is accomplished only after a prearranged time period aftersaid tim-ng control circuit is inactivated, and a timing. wavegenerating circuit coupled. to said timing control circuit to produce atiming wave havingy a number of cycles equal tothe number of elements ineach sig-nal character in response te the activation ot said timingcontrol circuit,l said timing control circuit. being inactivated on: thelast cycle of said timing wave.

5; A code signal regenerator having input ter.- ininais. to which codesignals as received are applied, a timing Wave genera-tor responsive tore.- ception of a single code signal element of given nature coupled tosaidy input terminals to produce" a train of timing. pulses, amark/space detector having a code signal element integrating circuitcoupled. to said input terminals and an output circuit from whichregenerated code sig,- nals are obtained coupled to said timing wavegenerator, and afalse start. detector having. an input circuit coupledyto the integrating circuit of said mark/spacedetector and an output circuit coupled to said timing wave generator to prevent operation of thelatter whenl said single code signal element is of nature. other thansaid given nature, the time constant of said false-start detector beingless than that of said mark/space detector tov prevent4 the latter fromproducing a regenerated code signal element. in the event that saidsingle code signal element is of nature other than saidgiven nature.

6. In a code signa-lf regenerator having input terminals to which codesignals as receivedrare applied andy outputv terminals at which saidcode signals as regenerated are available. anI output load resistorconnected tasaid output terminals, a plurality of electronA dischargedevices each havingl an anode: electrode, afcontrol. grid anda cathodeelectrode, one of said electrodes of each of saidy discharge devicesbeing connected to said` output load resistor, connections betweenanother of said electrodes of one of saiddis charge" devices and saidinput terminalsi a mark/space detector having an input circuit coupledto` said input terminals and an` output circuit coupledy to another ofsaid electrodes of another of said. discharge devices, andv meanscoupled to the control grids of said one and said other dischargedevices to couple said input terminals and saidoutput circuitofsaidmark/ space detector selectively to saidI load resistor.

7-. In any electronic circuit for regenerating telegraph signals,I apair of input terminals to Which said telegraph signals are applied agen-V erator coupled to said input terminals to produce a timing. wavesynchronized with said signals, and` a mark/space detector including afirst vacuum tube having a cathode, a control grid and an.v anode,aninput circuit coupled: between the grid; and cathode of said rirsttube and arranged to have said signals` applied thereto, a

signal element integrating. capacitor coupled to the anode of said tube,a:- secondv vacuum tube having. atleast a cathode, af-control grid and.an anode, the cathode of said second tube being connected'to the anodeof said iirst tube and one terminal of said capacitor,v the anodev ofsaid second tube being connectedtofthe other terminal of said capacitor,a. tlfiird vacuumtube. having a cathode, a control grid and an anode,said cathode being connected to said one terminal of said capacitor andthe anode being connected to a shunt resistor-capacitor combinationconstituting an output load impedance, a fourth vacuum tube having acathode, a control grid and an anode, the anode of said fourth tubebeing connected to the grid circuit oi said second vacuum tube, afurther vacuum tube having a cathode, a control grid and an anode,separate load resistors coupled to the anode and cathode respectively ofsaid further tube, the grid of said third vacuum tube being connectedvia diierentiating circuitry to the anode load resistor or said furthertube, the grid of said fourth tube being connected to the cathode loadresistor of said further tube, the grid of said iurther tube beingconnected to said timing wave generator, a time delay network interposedbetween said fourth vacuum tube and said further vacuum tube, thereby insequence to charge said signal element integrating capacitor to apotential indicative of the nature o the individual signal element underconsideration, to connect said capacitor through said third vacuum tubeto said output load impedance at the end of the signal element underconsideration to develop a pulse therein or polarity indicative ofelements of one nature only, and an additional vacuum tube having acathode, a grid and an anode, a resistor coupling the anode of saidadditional vacuum tube to the cathode oi said further vacuum tube and tothe grid of said fourth vacuum tube by Way of said time delay network, aconnection between the grid circuit or" said additional vacuum tube tosaid timing wave generator to clamp the grid of said second vacuum tubeat a positive potential to discharge said signal element integratingcapacitor in readiness Jfor the succeeding signal element, and tomaintain said capacitor discharged in readiness until the succeedingsignal element is applied` 8. A timing Wave generator for a start-stoptelegraph receiving system, including a two-terminal oscillator circuitand an oscillator control circuit comprising three electron dischargestructures each having cathode, grid and anode eiectrodes, resistorsconnecting the grid and cathode electrodes of said structures to a pointof negative potential, the grid electrode of one of said structuresbeing capacitively coupled to the anode electrode of another oi saidstructure, the grid electrode of said other structure being connected tothe cathode electrode or the further structure, a resistor connectingthe anode or said further structure to a point oi positive potential, atiming wave output load resistor connecting the anode electrode of saidone structure to a point of potential intermediate the rst said pointsof potential, a tuned circuit coupling the anode electrode or said otherstructure to said point of intermediate potential, and means to applypotentials to the grid electrode of said further structure to controlthe production of oscillations oi frequency determined by said tunedcircuit at said timing wave output load resistor.

9. A timing wave generator for a start-stop telegraph receiving system,including a two-terminal oscillator circuit and an oscillator controlcircuit comprising three electron discharge structures each havingcathode, grid and anode electrodes, resistors connecting the grid andcathode electrodes of said structures to a point of negative potential,the grid electrode of one of said structures being capacitively coupledto the anode electrode of another of said structure, the grid electrodeof said other structure being connected to the cathode electrode of thefurther structure, a resistor connecting the anode of said furtherstructure to a point oi positive potential, an output load resistorconnected to the anode electrode i' said one structure to a point ofpotential intermediate said points of potential, a tuned circuitcoupling the anode electrode or said other structure to said point ofintermediate potential, a tuning control circuit comprising a bistablere-ciproconductive circuit triggered to one stable state equilibrium byreceived telegraph signals, a connection from said bistablereciproconductive circuit to the grid electrode or" said furtherstructure to produce oscillations of frequency determined by said tunedcircuit at said output load resistor when said reciproconductive circuitin said one state oi equilibrium, a counting circuit coupled betweensaid output load resistor and said bistable reciproconductive circuit totrigger the latter to the other state of equilibrium thereby to ceaseproduc ion of oscillations at said output load resistor.

lo. ln an electronic telegraph signal regenerating circuit arrangementof the type having a inarii/ space detector and regenerator coupledbetween input terminals to which the signal elements as received areapplied and output terminals at which said signal elements are obtainedin :egenerated forni, a timing wave generator coupled to said inputterminals to produce a train o pulses synchronized with the reception ofsaid signal elements, a protective circuit connected across said outputterminals and coupled to said timing wave generator, said protectivecircuit comprising a bistable reciproconductive circuit coupled to saidtiming wave generator to be triggered to one state of equilibrium byapplication oi said pulses and arranged to be triggered to the otherstate ci equilibrium by the output of said mark/space detector applied-to said output terminals, an electron discharge tube having theanode-cathode path thereon connected across said output terminals andhaving a control grid element, a resistancecapacity network coupled tosaid grid element and having time constant greater than the tune periodbetween said pulses, connections from said timing Wave generator to saidgrid element to block said electron discharge tube on application ofsaid pulses, and connections between said bistable recipr conductivecircuit and said grid element to maintain said electron discharge tubeblocked only when the output of said mark/ space detector is ofpredetermined nature.

il. ln an electronic telegraph signal regenerating circuit arrangenientof the type having a mark/space detector and regenerator coupled betweeninput terminals to which the signal elements as received are applied andoutput terminais at which said signal elements are obtained inregenerated form a timing Wave generator coup'ied to said inputterminals to produce a train of pulses synchronized with the receptionof said signal elements, a protective circuit connected across outputterminals and coupled to said timing wave generator, said protectivecircuit comprising a bistable reciproconductive circuit o said timingwave generator to be triggered to one state of equilibrium byapplication of said pulses and arranged to be triggered to the otherstate or equilibrium by the output of said mark/space detector appliedto said output terminals, an electron discharge tube having theanode-cathode path thereof connected across said output terminals andhaving a control grid element, a resistance-capacity network coupled tosaid grid element and having a time constant greater than time periodbetween said pulses, a vacuum tube arranged to couple said timing wavegenerator to said grid element to block said electron discharge tube onapplication of said pulses to the control element of said vacuum tube,and another vacuum tube arranged between said bistable reciproconductivecircuit and said grid element to maintain said electron discharge tubeblocked only when the output of said mark/space detector at the end ofthe rlrst signal element is mark-ing.

12'. In a regenerator for a mark/space telegraph receiving systemincluding a pair of input.

terminals to which the signals are applied as received and a pair ofoutput terminals from which said signals are available lin regeneratedform a mark/space detector having an input circuit connected to saidinput terminals and an output circuit arranged to produce mark and spacesignals in accordance with the nature of the signals applied to theinput circuit, circuit selecting electronic switch including a pair ofelectron discharge tubes having the anodes connected to said outputterminals, control grids and cathodes, the cathode of one of said tubesbeing connected to the output circuit of said mark/space detector, thecathode of the other of said tubes being coupled to said inputterminals, the grid of said one tube being maintained at a potentialnormally rendering said one tube conducting to couple said mark/space.detector to said output terminals, a circuit selecting electronicswitch control circuit having a time delay network intei-posed thereinand Connected to the grid of said other tube, said switch controlcircuit being connected to said mark/space detector and responsive tosignals received therein to produce a potential of value and duration atwhich to maintain said other tube blocked when said received signals areof normal length and to permit said other tube to conduct when saidreceived signals are longer than normal.

13. An electronic circuit arrangement for regenerating xed length,mark/space, start-stop telegraph signals of the type having a stopsignal element longer than the other signal elements of each character,including a pair of input terminals to which the signals are applied asreceived and a pair of output terminals from which said signals areavailable in regenerated form, including a mark/space detector having aninput circuit coupled to said input terminals and an output circuitcomprising a bistable reciproconductive circuit arranged to produce markand space pulses in accordance with the nature of the signal elementsapplied to the input circuit of the mark/ space detector, circuitselecting electronic switch circuit arranged to couple said outputterminals selectively to said input terminals and to said bistablereciproconductive circuit, a timing control reciproconductive circuitarranged to be triggered to an active state in response to the receiptof the first signal element of each character, an electronic circuitselecting switch control circuit coupled to said timing controlreciproconductive circuit and said circuit selecting electronic switchcircuit to cause the latter electronic switch circuit to couple thei'lrst said reciproconductive circuit to said output terminals when saidtiming control reciproconductive circuit is active and to couple saidinput terminals 22 to said output terminals for direct operation whensaid timing control reciproconductive circuit is in the idle state, saidcircuit selecting switch control circuit incorporating a timedelaywhereby said coupling for direct operation is accomplished onlyafter a prearranged time period after said timing controlreciproconductive circuit is inactivated, a timing control failureelectronic switch connected across said output terminals and a timingcontrol failure switch control circuit incorporating another time delaycon-v nected between said; timing control reciproconductive circuit andsaid timing control failure' electronic switch and arranged to close thelatter electronic switch after another predetermined time period aftersaid timing control reciproconductive circuit is activated, said otherpredetermined time period` being greater than the time duration of onecharacter of said incoming signal, a detector failure electronic switchconnected across said output terminals and a detector failure switchcontrol circuit having a time delay connected between said timingcontrol reciproconductive circuit and said detector failure electronicswitch and arranged to close the latter electronic switch after aprearranged time period. after said timing control reciproconductivecircuit is activated, said prearranged time periodv being greater thanthe duration of one signal element of said incoming signal, and a timingwave generating circuit coupled to said timing control reciproconductivecircuit to produce a timing wave having a number of cycles equal to thenumber of elements in each signal character in re sponse to theactivation of saidA other reciproconductive circuit, said timing controlreciproconductive circuit being inactivated on the last cycle` of saidtiming wave.

lli. An electronic circuit arrangement for regenerating xed length,mark/space, start-stop telegraph signals of the type having a stopsignal element longer than the other signal elements of each character,including a pair of input terminals to which the signals are applied asreceived and a pair of output terminals from which said signals areavailable in regenerated form, including a mark/space detector having aninput circuit coupled to said input terminals and an output circuitcomprising a bistable reciproconductive circuit arranged to produce markand space pulses in accordance with the nature of the signal elementsapplied to the input circuit of the mark/space detector, circuitselecting electronic switch arranged to couple said output terminalsselectively to said input terminals and to said bistablereciproconductive circuit, a timing control circuit arranged to betriggered to an active state in response to the receipt of the firstsignal element of each character, a timing control electronic switchcontrol circuit coupled to said timing control circuit and said circuitselecting electronic switch to cause said circuit selecting electronicswitch to couple the rst said reciproconductive circuit to said outputterminals when said timing control circuit is active and to couple saidinput terminals to said output terminals for direct operation when saidtiming control circuit is in the idle state, timing control switchcontrol circuit incorporating a time delay whereby said couplingordirect operation is accomplished only after a prearranged time periodafter Said timing control circuit is inactivated, a detector failureelectronic switch connected across said output terminals and a detectorfailure switch control circuit incorporating another time delayconnected between said timing control circuit and said detector failureelectronic switch and arranged to close the latter electronic switchafter another predetermined time period after said timing controlcircuit is activated, said other predetermined time period being greaterthan the time duration of one char acter of said incoming signal, and atiming wave generating circuit coupled to said timing control circuit toproduce a timing Wave having a number of cycles equal to the number ofelements in each signal character in response to the activation of saidtiming control circuit, said timing control circuit being inactivated onthe last cycle of said timing wave.

15. A timing wave generator for a start-stop telegraph receiving system,including a bistable reciproeonductive control circuit arranged to betriggered to one state of equilibrium in response to an applied signaloi given nature, an oscillator circuit and an oscillator control circuitcomprising three electron discharge structures each having cathode, gridand anode electrodes, resistors connecting the grid and cathodeelectrodes of said structures to a point of negative potential, the gridelectrode of one oi said structures being capacitively coupled to theanode electrode of another of said structures, the grid electrode ofsaid other structure being connected to the cathode electrode of thefurther structure, a resistor connecting the anode of said furtherstructure to a point of positive potential, an output load resistorconnecting the anode electrode of said one structure to another point oipotential intermediate the first of said points of potential, a tunedcircuit coupling the anode electrode of said other structure to saidpoint of intermediate potential,

a connection from said bistable reciproconductive control circuit toapply potentials to the grid electrode of said further structure tocontrol the production of oscillations of frequency determined by saidtuned circuit at said output load resistor, a counting circuitcomprising a plurality of bistable reciproconductive circuits connectedin cascade between said output load resistor and said bistablereciproconductive control circuit to count the number of cycles ofoscillations produced by said oscillator and to trigger said bistablereciproconductive control circuit to the alternate state of equilibriumupon said count reaching a predetermined number, and a clamping circuitconnected between all of said reciproconductive counting circuits andsaid point of negative potential and responsive to the triggering orsaid reciproconductive control circuit to said one state to conditionsaid reciproconductive counting circuits in the proper phaserelationship for the counting operation.

References Cited in the i'lle of this patent UNITED STATES PATENTSNumber Name Date 2,404,047 Flory et al July 16, 1946 2,430,547 Andersonet al. Nov. 1l, 1947 2,454,089 Rea et al Nov. 16, 1948 2,474,490 PelleJune 28, 1949 2,536,035 Cleeton Jan. 2, 1951 2,536,578 Slayton Jan. 2,1951 FORETGN PATENTS Number Country Date 533,566 Great Britain Feb. 17,1941

